Distrait motor vehicle operators can forget to unplug an extension cord to the block heater of their vehicles before driving away. When this happens and the cord leading to the block heater is tied to the grille of the vehicle, damage to the grille can occur. In other instances, the extension cord can be lost at some distance from the operator's home, when it finally let go from the block heater cord. It is therefore desirable to warn a motor vehicle operator of such inadvertence before, or as soon as the vehicle's engine is started.
Engine block heater of the conventional type are described in U.S. Pat. No. 2,507,213 issued on May 9, 1950 to Roy H. McConnell, and in U.S. Pat. No. 5,210,393 issued on May 11, 1993 to Richard K. Shier. Each of these devices typically comprises an electrical heating element mounted to the engine block and extending into one of the cooling fluid passage of the engine block. An electrical cord is connected to the terminals of the electrical heating element, and extends from under the hood of the engine compartment for connection to a common electrical extension cord. These devices, however, are lacking a means for connection to an annunciator system of a vehicle, or to an alarm device to remind an operator to unplug the extension cord before starting the engine.
In other electrical circuits of vehicles, pilot lights are used to indicate to an operator when an engine warming device is in operation. Examples of these circuits are illustrated in the U.S. Pat. No. 2,129,571 issued on Sep. 6, 1938 to Joseph Driscoll, and in the U.S. Pat. No. 3,744,046 issued on Jul. 3, 1973 to Nick J. Tamasi. In the first case, the pilot light indicates an "ON" mode of a carburetor heater, and in the latter case, a series of indicator lights shows various operating conditions of an auxiliary heater for a diesel engine. In both cases, however, it is believed that the installations are complex and better done by an experienced auto-mechanic. Also, these circuits do not have any means to warn an operator of an energized block heater condition when an engine is started.
The unavailability of an alarm system for use in association with an engine block heater has contributed to the development of a market demand for a simple alarm system that is compatible to most vehicle configurations and that is susceptible of easy installation by a person having few tools and limited electrical and mechanical skills.